1. Field of the Invention
This invention relates to color diffusion transfer photographic products. More precisely, the invention relates to integral color diffusion transfer photographic film units and, in particular, to improved color diffusion transfer photographic film units capable of providing color prints which retain excellent whiteness in the frame portions of the prints over prolonged periods of time.
2. Description of the Prior Art
Recently, integral color diffusion transfer photographic film units have been developed comprising two dimensionally stable supports, at least one of them being transparent, and, laminated therebetween, a dye-receiving layer and at least one photosensitive silver halide emulsion layer having associated therewith a dye-image-providing material, said integral film unit having been joined together at at least one end thereof. Since the operation of viewing the images prepared therein by imagewise exposure and development using such a photographic film unit becomes simplified, the value of the photographic system for producing so-called one step photographs is now being recognized.
Integral diffusion transfer photographic film units are widely known in the art and are disclosed, for example, in U.S. Pat. Nos. 2,983,605, 3,415,644, 3,415,645, 3,415,646, 3,578,540, 3,573,043, 3,615,421, 3,594,164, 3,594,165, 3,620,724, 3,635,707, and 3,993,486, British Pat. Nos. 1,269,805 and 1,330,524, Japanese Patent Publication Nos. 21660/74 and 21661/74, Belgian Pat. Nos. 757,959 and 757,960, and West German Pat. No. 2,019,430.
Belgian Pat. No. 757,960 discloses a photographic film unit which is composed of a photosensitive sheet and an opaque cover sheet (having associated therewith a pH neutralization system) joined together at an end thereof, said photosensitive sheet comprising a transparent support, an image-receiving layer, a substantially opaque light-reflecting layer (e.g., a TiO.sub.2 layer and a carbon black layer), and at least one photosensitive silver halide emulsion layer having associated therewith a dye-image-providing material. After imagewise exposing the photosensitive sheet, the cover sheet is superposed on the photosensitive sheet in a face-to-face relationship, a processing composition is spread between them in order to conduct image development in the light, and the color images transferred in the image-receiving layer can thus be viewed through the transparent support.
Belgian Pat. No. 757,959 discloses a similar photographic film unit to that of Belgian Pat. No. 757,960, but the disclosure differs in that: (1) a transparent cover sheet is used, (2) a photosensitive sheet and the cover sheet are previously fixed at the three sides, (3) after imagewise exposing the photosensitive sheet through the transparent cover sheet, a developer containing an opacifying agent is spread therein from the other side to perform the development in the light, and (4) the color images transferred in the image-receiving layer are viewed through the transparent support.
The practical structures of these photographic film units are described in Japanese Application (OPI) Nos. 153628/75 and 153629/75 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application") and Japanese Patent Application (OPI) Nos. 33630/76 and 137411/76. These publications disclose that a photosensitive sheet and a cover sheet are joined together by adhesion at at least one end thereof through a sheet of a masking material and/or a railing material having on both surfaces thereof pressure-sensitive or heat-sensitive resins having a same or different composition. The masking material is usually in contact with the photosensitive sheet and the railing material in contact with the cover sheet but in an example disclosed therein, only a masking material is used, one surface of the masking material is in contact with the photosensitive sheet, and the other surface is in contact with the cover sheet. This masking material has the functions of maintaining the film unit in an integral state, preventing the processing solution (when the solution is spread in the film unit) from leaking outside the film unit, preventing at the same time the entrance of the processing solution into the peripheral portions of the film unit, and forming a white frame for the color print image formed by the transfer of color materials.
However, although the transfer color print obtained by such a system may have the beautiful white frame thereof directly after development, when the print is preserved for a long period of time, and particularly at a high temperature, the white frame of the print becomes discolor, which reduces greatly the quality of the transfer print.